Circuit arrangement, redox recycling sensor, sensor assembly and a method for processing a current signal provided by a sensor electrode

ABSTRACT

A circuit arrangement has a sensor electrode, a control circuit which is coupled to the sensor electrode via an input, and a current source which is coupled via a control input to a control output of the control circuit. The current source can be controlled by the control circuit. The control circuit is arranged so that if the current signal at its input is outside a predetermined current intensity range, the control circuit controls the current source so that the current source sets the electric current generated by it so that the electric current flowing into the input of the control circuit is brought to a predetermined current intensity value. Furthermore, the control circuit is set up in such a way that if the current signal at its input is within the predetermined current intensity range, the control circuit controls the current source so that the current source holds the electric current generated by it at the present value. Furthermore, the circuit arrangement has a detection unit which can detect the event that the current signal flowing into the control circuit via its input is outside the predetermined current intensity range.

The invention relates to a circuit arrangement, a redox recyclingsensor, a sensor arrangement and a method for processing a currentsignal provided via a sensor electrode.

FIG. 2A and FIG. 2B show a biosensor chip, as described in [1]. Thesensor 200 has two electrodes 201, 202 made of gold, which are embeddedin an insulator layer 203 made of electrically insulating material.Connected to the electrodes 201, 202 are electrode terminals 204, 205,by means of which the electronic potential present at the electrode 201,202 can be supplied. The electrodes 201, 202 are configured as planarelectrodes. DNA probe molecules 206 (also referred to as capturemolecules) are immobilized on each electrode 201, 203 (cf. FIG. 2A). Theimmobilization is effected in accordance with the gold-sulfur coupling.The analyte to be investigated, for example an electrolyte 207, isapplied on the electrodes 201, 202.

If the electrolyte 207 contains DNA strands 208 with a base sequencewhich is complementary to the sequence of the DNA probe molecules 206,i.e. which sterically match the capture molecules in accordance with thekey/lock principle, then these DNA strands 208 hybridize with the DNAprobe molecules 206 (cf. FIG. 2B).

Hybridization of a DNA probe molecule 206 and a DNA strand 208 takesplace only when the sequences of the respective DNA probe molecule andof the corresponding DNA strand 208 are complementary to one another. Ifthis is not the case, then no hybridization takes place. Thus, a DNAprobe molecule having a predetermined sequence is in each case onlycapable of binding a specific DNA strand, namely the one with arespectively complementary sequence, i.e. of hybridizing with it, whichresults in the high degree of selectivity of the sensor 200.

If hybridization takes place, then the value of the impedance betweenthe electrodes 201 and 202 changes, as can be seen from FIG. 2B. Thischanged impedance is detected by applying a suitable electrical voltageto the electrode terminals 204, 205 and by registering the currentresulting from this.

In the case of hybridization, the capacitive component of the impedancebetween the electrodes 201, 202 decreases. This can be attributed to thefact that both the DNA probe molecules 206 and the DNA strands 208,which possibly hybridize with the DNA probe molecules 206, areelectrically nonconductive and thus, as can be seen, in partelectrically shield the respective electrode 201, 202.

In order to improve the measurement accuracy, it is known from [2] touse a plurality of electrode pairs 201, 202 and to arrange the latter inparallel with one another, these being arranged intermeshed with oneanother, as can be seen, so that the result is a so-called interdigitalelectrode 300, FIG. 3A showing the plan view thereof and FIG. 3B showingthe cross-sectional view thereof along the section line I-I′ from FIG.3A. The dimensioning of the electrodes and the distances between theelectrodes are of the order of magnitude of the length of the moleculesto be detected, i.e. the DNA strands 208, or less, for example in theregion of 200 nm or less.

Furthermore, principles relating to a reduction/oxidation recyclingprocess for registering macromolecular biomolecules are known forexample from [1], [3]. The reduction/oxidation recycling process, alsoreferred to hereinafter as the redox recycling process, will beexplained in more detail below with reference to FIG. 4A, FIG. 4B, FIG.4C.

FIG. 4A shows a biosensor 400 having a first electrode 401 and a secondelectrode 402, which are applied on an insulator layer 403. A holdingregion 404 is applied on the first electrode 401 made of gold. Theholding region 404 serves for immobilizing DNA probe molecules 405 onthe first electrode 401. Such a holding region is not provided on thesecond electrode 402.

If DNA strands 407 having a sequence which is complementary to thesequence of the immobilized DNA probe molecules 405 are intended to beregistered by means of the biosensor 400, then the sensor 400 is broughtinto contact with a solution to be investigated, for example anelectrolyte 406, in such a way that DNA strands 407 possibly containedin the solution 406 to be investigated can hybridize with thecomplementary sequence to the sequence of the DNA probe molecules 405.

FIG. 4B shows the case where the DNA strands 407 to be registered arecontained in the solution 406 to be investigated and have hybridizedwith the DNA probe molecules 405.

The DNA strands 407 in the solution to be investigated are marked withan enzyme 408, with which it is possible to cleave molecules describedbelow into electrically charged partial molecules. It is customary toprovide a considerably larger number of DNA probe molecules 405 thanthere are DNA strands 407 to be determined contained in the solution 406to be investigated.

After the DNA strands 407 possibly contained in the solution 406 to beinvestigated, together with the enzyme 408, are hybridized with theimmobilized DNA probe molecules 405, the biosensor 400 is rinsed, as aresult of which the nonhybridized DNA strands are removed and thebiosensor chip 400 is cleaned of the solution 406 to be investigated.The rinsing solution used for rinsing or a further solution suppliedseparately in a further phase has an electrically uncharged substanceadded to it, which contains molecules that can be cleaved by means ofthe enzyme 408 at the hybridized DNA strands 407, into a first partialmolecule 410 having a negative electrical charge and into a secondmolecule having a positive electrical charge.

As shown in FIG. 4C, the negatively charged first partial molecules 410are attracted to the positively charged first electrode 401, which isindicated by means of the arrow 411 in FIG. 4C. The negatively chargedfirst partial molecules 410 are oxidized at the electrode 401, which hasa positive electrical potential, and are attracted as oxidized partialmolecules 413 to the negatively charged second electrode 402, where theyare reduced again. The reduced partial molecules 414 again migrate tothe positively charged first electrode 401. In this way, an electriccirculating current is generated, which is proportional to the number ofcharge carriers respectively generated by means of the enzymes 406.

The electrical parameter which is evaluated in this method is the changein the electric current m=dI/dt as a function of the time t, as isillustrated schematically in the diagram 500 in FIG. 5.

FIG. 5 shows the function of the electric current 501 depending on thetime 502. The resulting curve profile 503 has an offset currentI_(offset) 504, which is independent of the temporal profile. The offsetcurrent I_(offset) 504 is generated on account of non-idealities of thebiosensor 400. An essential cause of the offset current I_(offset)resides in the fact that the covering of the first electrode 401 withthe DNA probe molecules 405 is not effected in an ideal manner, i.e. notcompletely densely. In the case of a completely dense coverage of thefirst electrode 401 with the DNA probe molecules 405, an essentiallycapacitive electrical coupling would result on account of the so-calleddouble-layer capacitance, which is produced by the immobilized DNA probemolecules 405, between the first electrode 401 and the electricallyconductive solution 406 to be investigated. However, the incompletecoverage leads to parasitic current paths between the first electrode401 and the solution 406 to be investigated, which inter alia also haveresistive components.

However, in order to enable the oxidation/reduction process, thecoverage of the first electrode 401 with the DNA probe molecules 405 isintended not to be complete at all, in order that the electricallycharged partial molecules, i.e. the negatively charged first partialmolecules 410, can pass to the first electrode 401 on account of anelectrical force. In order, on the other hand, to achieve the greatestpossible sensitivity of such a biosensor, and in order simultaneously toachieve the least possible parasitic effects, the coverage of the firstelectrode 401 with DNA probe molecules 405 should be sufficiently dense.In order to achieve a high reproducibility of the measured valuesdetermined by means of such a biosensor 400, both electrodes 401, 402are intended always to provide an adequately large area afforded for theoxidation/reduction process in the context of the redox recyclingprocess.

Macromolecular biomolecules are to be understood for example as proteinsor peptides or else DNA strands having a respectively predeterminedsequence. If proteins or peptides are intended to be registered asmacromolecular biomolecules, then the first molecules and the secondmolecules are ligands, for example active substances with a possiblebinding activity, which bind the proteins or peptides to be registeredto the respective electrode on which the corresponding ligands arearranged.

Examples of ligands that may be used are enzyme agonists,pharmaceuticals, sugars or antibodies or some other molecule which hasthe capability of specifically binding proteins or peptides.

If the macromolecular biomolecules used are DNA strands having apredetermined sequence which are intended to be registered by means ofthe biosensor, then it is possible, by means of the biosensor, for DNAstrands having a predetermined sequence to be hybridized with DNA probemolecules having the sequence that is complementary to the sequence ofthe DNA strands as molecules on the first electrode.

A probe molecule (also called capture molecule) is to be understood as aligand or a DNA probe molecule.

The value m=dI/dt introduced above, which corresponds to the gradient ofthe straight line 503 from FIG. 5, is proportional to the electrode areaof the electrodes used for registering the measurement current.Therefore, the value m is proportional to the longitudinal extent of theelectrodes used, for example in the case of the first electrode 201 andthe second electrode 202 proportional to the length thereofperpendicular to the plane of the drawing in FIG. 2A and FIG. 2B. If aplurality of electrodes are connected in parallel, for example in theknown interdigital electrode arrangement (cf. FIG. 3A, FIG. 3B), thenthe change in the measurement current is proportional to the number ofelectrodes respectively connected in parallel.

However, the value of the change in the measurement current may have arange of values that fluctuates to a very great extent, on account ofvarious influences, the current range that can be detected by a sensorbeing referred to as the dynamic range. A current intensity range offive decades is often mentioned as a desirable dynamic range. Causes ofthe great fluctuations may be, in addition to the sensor geometry, alsobiochemical boundary conditions. Thus, it is possible thatmacromolecular biomolecules of different types to be registered willbring about greatly different ranges of values for the resultingmeasurement signal, i.e. in particular the measurement current and thetemporal change thereof, which in turn leads to a widening of therequired overall dynamic range with corresponding requirements for apredetermined electrode configuration with downstream uniformmeasurement electronics.

The requirements made of the large dynamic range of such a circuit havethe effect that the measurement electronics are expensive andcomplicated in their configuration, in order to operate sufficientlyaccurately and reliably in the required dynamic range.

Furthermore, the offset current I_(offset) is often much greater thanthe temporal change in the measurement current m over the entiremeasurement duration. In such a scenario, it is necessary, within alarge signal, to measure a very small time-dependent change with highaccuracy. This makes very high requirements of the measurementinstruments used, which makes the registering of the measurement currentcomplex, complicated and expensive. This fact is also at odds with aminiaturization of sensor arrangements that is striven for.

To summarize, the requirements made of the dynamic range and thereforeof the quality of a circuit for detecting sensor events are extremelyhigh.

It is known, during circuit design, to take account of thenon-idealities of the components used (noise, parameter variations) inthe form such that an operating point at which these non-idealities playa part that is as negligible as possible is chosen for these componentsin the circuit.

If a circuit is intended to be operated over a large dynamic range,maintaining an optimum operating point over all the ranges becomesincreasingly more difficult, more complex and thus more expensive,however.

Small signal currents that are obtained at a sensor, for example, can beraised with the aid of amplifier circuits to a level that permits thesignal current to be forwarded for example to an external device orinternal quantification.

A digital interface between the sensor and the evaluating system isadvantageous for reasons of interference immunity and user-friendliness.Thus, the analog measurement currents are intended to be converted intodigital signals actually in the vicinity of the sensor, which can beeffected by means of an integrated analog-to-digital converter (ADC).Such an integrated concept for digitizing an analog small current signalis described in [4], for example.

In order to achieve the required dynamic range, the ADC should have acorrespondingly high resolution and a sufficiently high signal-to-noiseratio. Integrating such an analog-to-digital converter in directproximity to a sensor electrode furthermore constitutes a hightechnological challenge, and the corresponding process implementation iscomplex and expensive. Furthermore, achieving a sufficiently highsignal-to-noise ratio in the sensor is extremely difficult.

The invention is based on the problem of providing an error-robustcircuit arrangement with an improved detection sensitivity for electriccurrents that are very weakly variable with respect to time.

The problem is solved by means of a circuit arrangement, a redoxrecycling sensor, a sensor arrangement and a method for processing acurrent signal provided via a sensor electrode having the features inaccordance with the independent patent claims.

The invention provides a circuit arrangement having a sensor electrode,a control circuit, which is coupled to the sensor electrode via aninput, and a current source, which is coupled via its control input to acontrol output of the control circuit in such a way that the currentsource can be controlled by the control circuit, and which is coupled tothe sensor electrode via its output. The control circuit is set up insuch a way that if the current signal flowing into the control circuitvia its input is outside a predetermined current intensity range, thecontrol circuit controls the current source in such a way that thecurrent source sets the electric current generated by it in such a waythat the electric current flowing into the input of the control circuitis brought to a predetermined current intensity value. Furthermore, thecontrol circuit is set up in such a way that if the current signalflowing into the control circuit via its input is within thepredetermined current intensity range, the control circuit controls thecurrent source in such a way that the current source holds the electriccurrent generated by it at the present value. Furthermore, the circuitarrangement has a detection unit which can detect the event that thecurrent signal flowing into the control circuit via its input is outsidethe predetermined current intensity range.

Clearly, a sensor event takes place at the sensor electrode, e.g. thehybridization of a DNA strand with an enzyme label at a capture moleculeimmobilized on the sensor electrode, the enzyme generating free chargecarriers that bring about a current flow at the sensor electrode when acorrespondingly suitable liquid is added. This brings about atime-dependent change in the sensor current at the sensor electrode, asshown for example in FIG. 5. This sensor current I_(Sensor)characteristically influences the current I_(Meas) flowing via the inputof the control circuit. The control circuit is set up in such a way thatif the current I_(Meas) flowing via its input is outside thepredetermined current intensity range, the control circuit, via itscontrol output, provides the control input of the current source with asignal such that the current source provides, at its output, a currentvalue I_(Range) such that the current intensity I_(Meas) flowing via theinput of the control circuit is brought to the predetermined currentintensity value. A detection unit, which is preferably coupled to thecontrol circuit, detects the event that the current signal I_(Meas)flowing into the control circuit via its input is outside thepredetermined current intensity range. If by contrast, the currentsignal flowing into the control circuit via its input lies within thepredetermined current intensity range, then the control circuitgenerates, at its control output, a corresponding signal that isprovided to the control input of the current source and causes thelatter to hold the current I_(Range) generated by it at the present,constant value. Clearly, a detection signal is generated upon eachfurther rise in the sensor current I_(Sensor) by a predetermined currentinterval, so that a sensor event of a sensor electrode is registered inthis way.

In other words, the signal processing of very small currents in thepA-nA range is realized according to the invention, the analog currentsignal I_(Sensor) being converted into a sequence of detection signals,for example pulses, in direct proximity to the sensor. In other words, adigitization is effected by means of the analog current signalI_(Sensor) being converted into a temporal sequence of detectionsignals, preferably into a frequency. On account of the signalprocessing in direct proximity to the sensor, disturbing influences onthe path of the sensor signal to a signal processing unit are avoided orkept down, which results in a high signal-to-noise ratio. In otherwords, the useful signal is filtered out from the sensor signal indirect proximity to the sensor.

Furthermore, it is advantageous that, by means of the circuitarrangement according to the invention, the sensitivity and the dynamicrange of the sensor or the signal processing unit can be set flexibly tothe requirements of the individual case. As shown in FIG. 5, for examplein the case of detecting DNA strands using the redox recyclingprinciple, the hybridization events are converted into a signal currentthat rises in constant fashion with respect to time. The sensitivity anddynamic range can be adjusted by setting the measurement time and bysetting the predetermined current intensity range which, whenrespectively exceeded, respectively triggers a detection pulse. Adesired dynamic span of five decades (for example for registeringelectric currents of between 1 pA and 100 nA) can therefore be realizedvery simply according to the invention.

In accordance with an advantageous development of the circuitarrangement according to the invention, said circuit arrangementfurthermore has a counter element, which is electrically coupled to thedetection unit and which is set up in such a way that it counts thenumber and/or the temporal sequence of the events detected by thedetection unit.

Preferably, the counter element is set up in such a way that if theelectric current flowing into the input of the control circuit exceedsan upper limit of the predetermined current intensity range, the counterreading is increased by a predetermined value. By contrast, if theelectric current flowing into the input of the control circuit fallsbelow a lower limit of the predetermined current intensity range, thecounter reading is preferably decreased by a predetermined value.

The described functionality of the counter element corresponds to thescenario where the sensor current has a sign such that it isprogressively increased on account of a sensor event of the sensorcurrent I_(Sensor). Each time the predetermined current intensity rangeis exceeded, the counter reading is clearly increased by a predeterminedvalue (preferably by “1”), whereas each time the predetermined range isundershot, the counter reading is decreased by a predetermined value(preferably by “1”).

In the case of a scenario that is complementary thereto, in which thesensor current has a sign such that the current I_(Sensor) isprogressively decreased on account of a sensor event, the counterelement is set up in such a way that if the electric current flowinginto the input of the control circuit exceeds an upper limit of thepredetermined current intensity range, the counter reading is decreasedby a predetermined value, and that if the electric current flowing intothe input of the control circuit falls below a lower limit of thepredetermined current intensity range, the counter reading is increasedby a predetermined value.

The lowering of the current value in a scenario in which a detectionevent increases the current value of a sensor electrode can beattributed for example to interfering and parasitic events, such asnoise events, etc.

It is advantageous that, according to the invention, the detectorselectively detects the situation of the predetermined current intensityrange being exceeded or undershot and consequently either increments ordecrements the counter reading of the counter element.

In other words, the signal is automatically averaged and errors onaccount of noise effects, etc. are thereby compensated for. This leadsto an increase in the detection sensitivity.

Preferably, the current source is a voltage-controlled current source.

Furthermore, the control circuit preferably has, at its input, acurrent-voltage converter set up in such a way that the current presentat the input of the control circuit is converted into an electricalvoltage signal by means of the current-voltage converter.

In accordance with an advantageous development of the circuitarrangement according to the invention, said circuit arrangement isdesigned as an integrated circuit.

The integration of the circuit arrangement, for example into a siliconsubstrate (e.g. a chip in a wafer), brings about a high detectionaccuracy on account of the current signal processing on-chip. Thecurrent is processed on the chip directly and in direct proximity to thesensor electrode, thereby avoiding disturbing signals such as anadditional noise on account of an increased communication path.Furthermore, it is advantageous that the dimensioning of the circuitarrangement can be reduced on account of the integration of the circuitarrangement according to the invention, for example into a semiconductorsubstrate. This miniaturization leads to a cost advantage sincemicroscopic measurement equipment is obviated.

It must be emphasized that, on account of the integration of the circuitarrangement according to the invention into a semiconductor substratethe circuit arrangement can be produced using processes of semiconductortechnology that are standardized and widespread, as well as beingmature, which brings about quality and cost advantages.

Furthermore, the invention provides a redox recycling sensor having acircuit arrangement having the features described above.

The sensitivity of the circuit arrangement according to the invention issufficiently high, as described, to be able to register very smallelectric currents such as usually arise during the detection ofbiomolecules of low concentration. Therefore, the circuit arrangement ofthe invention is preferably designed as a redox recycling sensor havingthe features described above with reference to FIG. 4A, FIG. 4B, FIG.4C.

Moreover, the invention provides a sensor arrangement having a pluralityof circuit arrangements having the features described. In particular,each of the circuit arrangements of the sensor arrangements may bedesigned as a redox recycling sensor.

Arranging a plurality of circuit arrangements for forming a sensorarrangement for example in an essentially matrix-type arrangementenables for example a parallel analysis of a liquid to be investigated.If said liquid contains different biomolecules, for example, such asdifferent DNA half strands, for example, and if different types ofcapture molecules are immobilized on the different sensor electrodes ofthe sensor arrangement, then the different DNA half strands can bedetected temporally in parallel. In many technical fields, the parallelanalysis is a desirable rationalization measure which saves operatingtime and thus costs. Therefore, a time-saving analysis of a liquid to beinvestigated is realized according to the invention.

The method according to the invention for processing a current signalprovided via a sensor electrode is described in more detail below.Refinements of the circuit arrangement according to the invention, ofthe redox recycling sensor according to the invention and of the sensorarrangement according to the invention also apply to the method forprocessing a current signal provided via a sensor electrode.

The method for processing a current signal provided via a sensorelectrode is effected using a circuit arrangement having the featuresdescribed above.

In accordance with the method, if the current signal flowing into thecontrol circuit via its input is outside the predetermined currentintensity range, the current source is controlled by the control circuitin such a way that the current source sets the electric currentgenerated by it in such a way that the electric current flowing into theinput of the control circuit is brought to the predetermined currentintensity value. By contrast, if the current signal flowing into theinput of the control circuit is within the predetermined currentintensity range, the control circuit controls the current source in sucha way that the current source holds the electric current generated by itat the present value. Furthermore, the detection unit detects the eventthat the current signal flowing into the control circuit via its inputis outside the predetermined current intensity range.

In accordance with an advantageous development, the number and/or thetemporal sequence of the events is counted by means of a counter elementthat is electrically coupled to the control circuit.

In accordance with a first alternative, if the electric current flowinginto the input of the control circuit exceeds an upper limit of thepredetermined current intensity range, the counter reading is increasedby a predetermined value. By contrast, if the electric current flowinginto the input of the control circuit falls below a lower limit of thepredetermined current intensity range, the counter reading is decreasedby a predetermined value.

In accordance with an alternative advantageous refinement, if theelectric current flowing into the input of the control circuit exceedsan upper limit of the predetermined current intensity range, the counterreading is decreased by a predetermined value, and, if the electriccurrent flowing into the input of the control circuit falls below alower limit of the predetermined current intensity range, the counterreading is increased by a predetermined value.

Exemplary embodiments of the invention are illustrated in the figuresand are explained in more detail below.

In the figures:

FIG. 1 shows a schematic view of a circuit arrangement in accordancewith a first exemplary embodiment of the invention,

FIG. 2A shows a cross-sectional view of a sensor in accordance with theprior art in a first operating state,

FIG. 2B shows a cross-sectional view of the sensor in accordance withthe prior art in a second operating state,

FIG. 3A shows a plan view of interdigital electrodes in accordance withthe prior art,

FIG. 3B shows a cross-sectional view along the section line I-I′ of theinterdigital electrodes in accordance with the prior art as shown inFIG. 3A,

FIG. 4A shows a biosensor based on the principle of redox recycling in afirst operating state in accordance with the prior art,

FIG. 4B shows a biosensor based on the principle of redox recycling in asecond operating state in accordance with the prior art,

FIG. 4C shows a biosensor based on the principle of redox recycling in athird operating state in accordance with the prior art,

FIG. 5 shows a functional profile of a sensor current in the context ofa redox recycling process,

FIG. 6 shows a detailed view of the functional profile of a sensorcurrent in the context of a redox recycling process,

FIG. 7 shows a schematic view of a circuit arrangement in accordancewith a second exemplary embodiment of the invention,

FIG. 8A shows a diagram schematically showing the dependence of thesensor current I_(Sensor) on the time t for the sensor electrode shownin FIG. 7,

FIG. 8B shows a diagram schematically showing the dependence of themeasurement current I_(Meas) on the time t for the diagram illustratedin FIG. 8A,

FIG. 9A shows a schematic view of a circuit arrangement in accordancewith a third exemplary embodiment of the invention,

FIG. 9B shows a diagram schematically showing the dependence of themeasurement current I_(Meas) on the time t for the diagram illustratedin FIG. 8A and for the third exemplary embodiment of the circuitarrangement of the invention as shown in FIG. 9A,

FIG. 10A shows a schematic view of a circuit arrangement in accordancewith a fourth exemplary embodiment of the invention,

FIG. 10B shows a schematic sketch of the detection unit of the fourthexemplary embodiment of the circuit arrangement of the invention asshown in FIG. 10A.

Clearly, the invention provides inter alia an on-chip integrated circuitconcept for directly converting a sensor signal of an electronicbiosensor based on the principle of redox recycling into frequencies.The signal that carries this frequency is present in the form of binarysignals with digital levels.

A basic idea for the invention's frequency conversion of a sensorcurrent signal, which is realized by means of the circuit arrangementaccording to the invention, is shown schematically in FIG. 6 on thebasis of a diagram 600.

The diagram 600 shown in FIG. 6 has an abscissa 602, along which thetime t is plotted. The sensor current I_(Sensor) is plotted along theordinate 601 of the diagram 600. Furthermore, a current-time curveprofile 603 is shown. An offset current I_(Offset) 604 is furthermoreentered into the diagram 600 from FIG. 6.

Proceeding from a current value I₀ at a first instant to, the currentaxis 601 is conceptually divided into equidistant segments of magnitudeΔI. In the time interval between the first instant t₀ and the secondinstant t₁, the current-time curve profile 603 sweeps over n currentintervals ΔI, as shown. The invention detects in a suitable manner howmany complete segments n and therefore what current interval nΔI areswept over by the sensor current I_(Sensor) in the time interval betweenthe first instant t₀ and the second instant t₁. Referring to thenomenclature introduced above, the metrologically relevant variable isthe current rise m 605, i.e. the sensor current I₁ at the second instantt₁ minus the sensor current I₀ at the first instant t₀ divided by thetime interval t₁-t₀ swept over (for a current that rises linearly withtime):m=(I ₁ −I ₀)/(t ₁ −t ₀)  (1)

On account of the subdivision of the current axis into segments ΔI andon account of the detection of the situation of a further interval ΔIrespectively being exceeded, what actually is registered is, a variablem* described by the following expression:m*(t ₁)=nΔI/(t ₁ −t ₀)  (2)

For the relative error on account of the quantization of the currentinto current intervals ΔI of finite width, the following expression iscrucial:(m−m*)/m=1/(n+1)  (3)

It can be seen from (3) that if n is chosen to be sufficiently large(i.e. if a measurement time is sufficiently long or if the currentinterval ΔI is chosen to be sufficiently small), the relative error canbe kept comparatively small. The following holds true to anapproximation for n:n=(I ₁ −I ₀)/ΔI  (4)

Consequently, it is possible, by means of a suitable choice of theinterval ΔI, to attain configurations which lead to sufficiently largevalues n over a dynamic range of the sensor signal, so that the residualcharacterization error is negligibly small.

A description is given below, with reference to FIG. 1, of a circuitarrangement 100—based on the principle described—in accordance with afirst preferred exemplary embodiment of the invention.

The circuit arrangement 100 has a sensor electrode 101, a controlcircuit 102, which is coupled via an input 103 to the sensor electrode101, and a current source 104, which is coupled via its control input105 to a control output 106 of the control circuit 102 in such a waythat the current source 104 can be controlled by the control circuit102, and which is coupled via its output 107 to the sensor electrode101. The control circuit 102 is set up in such a way that if the firstcurrent signal 108 flowing into the control circuit 102 via its input103 is outside a predetermined current intensity range, the controlcircuit 102 controls the current source 104 in such a way that thecurrent source 104 sets the second current signal 109 generated by it insuch a way that the first current signal 108 flowing into the input 103of the control circuit 102 is brought to a predetermined currentintensity value. Furthermore, the control circuit 102 is set up in sucha way that if the first current signal 108 flowing into the controlcircuit 102 via its input 103 is within the predetermined currentintensity range, the control circuit 102 controls the current source 104in such a way that the current source 104 holds the second currentsignal 109 generated by it at the present value. Furthermore, thecircuit arrangement 100 has a detection unit 110, which can detect theevent that the first current signal 108 flowing into the control circuit102 via its input 103 is outside the predetermined current intensityrange.

Furthermore, FIG. 1 shows capture molecules 111 immobilized at thesensor electrode 101. Furthermore, the illustration shows molecules 112with an enzyme label 113 which are to be registered and have hybridizedwith said capture molecules 111. The system—based on the principle ofredox recycling—of the sensor electrode 101, the capture molecules 111,the molecules 112 with their enzyme labels 113 which are to beregistered, etc. has the effect that electrically charged particles 114are generated, which effect a third current signal 115 of the sensorelectrode 101. This third current signal 115, which corresponds to thecurrent-time curve profile 603 illustrated in FIG. 6, contains theinformation of what number of particles 113 to be registered havehybridized with the capture molecules 111 on the surface of the sensorelectrode 101. The circuit arrangement 100 makes it possible to filterout the sensor information from the third current signal 115.

The precise functionality of the circuit arrangement of the invention isdescribed below with reference to FIG. 7, which shows a circuitarrangement 700 in accordance with a second exemplary embodiment of theinvention.

The circuit arrangement 700 has a sensor electrode 701, a controlcircuit 702, which is coupled via an input 703 to the sensor electrode701, and a current source 204, which can be controlled, via its controlinput 705, by the control output 706 of the control circuit 702 and iscoupled via its output 707 to the sensor electrode 701. The controlcircuit 702 is set up in such a way that if the measurement currentsignal I_(Meas) 708 flowing into the control circuit 702 via its input703 is outside a predetermined current intensity range, the controlcircuit 702 controls the current source 704 in such a way that thecurrent source 704 sets the auxiliary current signal I_(Range) 709generated by it in such a way that the measurement current signalI_(Meas) 708 flowing into the input 703 of the control circuit 702 isbrought to a predetermined current intensity value I_(Base) 710.Furthermore, the control circuit 702 is set up in such a way that if themeasurement current signal 708 flowing into the control circuit 702 viaits input 703 is within the predetermined current intensity range, thecontrol circuit 702 controls the current source 704 in such a way thatthe current source 704 holds the auxiliary current signal 709 generatedby it at the present value. Furthermore, the circuit arrangement 700 hasa detection unit 711, which can detect the event that the measurementcurrent signal 708 flowing into the control circuit 702 via its input703 is outside the predetermined current intensity range.

The predetermined current intensity range is monitored by means of athreshold value detector 712 of the control circuit 702. In accordancewith the exemplary embodiment of the circuit arrangement 700 as shown inFIG. 7, the predetermined current intensity range, that is to say therange between I_(Base) and I_(Base)+ΔI, is provided with the referencenumeral 713.

Furthermore, FIG. 7 shows a counter element 714 which is electricallycoupled to the detection unit 711 and is set up in such a way that itcounts the number and the temporal sequence of the events detected bythe detection unit 711. In particular, the counter element 714 is set upin such a way that if the electric current flowing into the input 703 ofthe control circuit 702 exceeds the upper limit I_(Base)+ΔI, the counterreading is increased by the predetermined value “1”.

Moreover, FIG. 7 shows the sensor current signal I_(Sensor) 715generated on account of sensor events at the sensor electrode 701.

Furthermore, FIG. 7 shows, in diagrams 716, 717, 718, the time profilesof the measurement current signal 708 (diagram 716), of the auxiliarycurrent signal 709 (diagram 717) and of the sensor current signal 715(diagram 718).

It must be emphasized that the diagrams 716 and 717 show an ideallydesirable time dependence of the measurement current signal 708 andauxiliary current signal 709, respectively, whereas the diagrams 719 and728 show a real time dependence of the measurement current signal 708and auxiliary current signal 709, respectively. By means of a suitablechoice of the components of the circuit arrangement 700 and of theoperating method, however, it is possible to approximate the real timedependence of the measurement current signal (diagram 719) and of theauxiliary current signal 709 (diagram 717) to the ideal profile of themeasurement current signal 708 (diagram 716) and auxiliary currentsignal 709 (diagram 717). For the purpose of a clear, simplifieddescription of the functionality of the components of the circuitarrangement 700 a description is given below of the case where themeasurement current signal 708 and the auxiliary current signal 709,respectively, can be described by means of an ideal profile as shown indiagram 716 and diagram 717, respectively.

The current source 704 shown in FIG. 7 is a voltage-controlled currentsource.

In the case of the circuit arrangement 700, the control circuit 702 has,at its input 703, a current-voltage converter 720 that is set up in sucha way that the measurement current signal 708 present at the input 703of the control circuit 702 is converted into an electrical voltagesignal by means of the current-voltage converter 720.

The components of the circuit arrangement 700 are integrated into asilicon substrate (not shown in FIG. 7), or a portion of the componentsis formed on the silicon substrate.

The circuit concept shown in FIG. 7 represents a realization of theprinciple according to the invention. The circuit idea is based on theuse of three current signals, I_(Meas) 708, I_(Range) 709 and I_(Sensor)715, that are linked to one another via an electrical node 721.

The sensor current I_(Sensor) 715 designates the electric current thatflows proceeding from the sensor electrode 701 on account of sensorevents effected on the sensor electrode 701 (cf. FIG. 1). A typical timedependence of the sensor current I_(Sensor) 715 is shown in the diagram718. The time dependence shown therein essentially corresponds to thecurrent-time curve profile 603 described above with reference to FIG. 6.Such a curve is obtained for example in the case of a detection inaccordance with the redox recycling method. The diagram 718schematically shows that the sensor current I_(Sensor) 715 isconceptually divided into intervals ΔI.

The measurement current signal I_(Meas) 708 is characterized in thatsaid electric current is limited to a fixed current range betweenI_(Base) and I_(Base)+ΔI. This current range is the predeterminedcurrent intensity range 713. If the measurement current signal I_(Meas)708 reaches the upper threshold I_(Base)+ΔI, as shown in diagram 716,then according to the invention the auxiliary current signal I_(Range)709 is set by means of the control circuit 702 to a current value suchthat the measurement current signal I_(Meas) 708 is brought back to thelower end of the current range, i.e. to the predetermined currentintensity value I_(Base) 710. In other words, the auxiliary currentsignal I_(Range) 709 serves for limiting the measurement current signalI_(Meas) 708 to the predetermined interval 713 by taking up currentcomponents that go beyond the threshold of this channel.

In accordance with the exemplary embodiment of the circuit arrangement700 as shown in FIG. 7, 0A is chosen as a value for the predeterminedcurrent intensity value I_(Base) 700. However, the choice of apredetermined current intensity value I_(Base) 710 that deviates fromthe current value 0A may be expedient in other configurations of thecircuit arrangement according to the invention.

On account of the three current signals 708, 709, 715 converging at theelectrical node 721, the following holds true:I _(Sensor) =I _(Meas) +I _(Range)  (5)

The functionality of the circuit arrangement 700 described below has theeffect that the information relevant to the analysis of the sensorevents with regard to the current rise m is contained in the measurementcurrent signal I_(Meas 708), whereas the auxiliary current signalI_(Range) 709 fulfils an auxiliary function.

Two operating states of the circuit arrangement 700 are explained below:

The following holds true in a first operating state (1):I _(Meas)(t)=I _(Sensor)(t)−I _(Sensor)(t′)+I _(Base)  (6a)I _(Range)(t)=I _(Sensor)(t′)−I _(Base)  (6b)

The following holds true in a second operating state (2):I _(Meas)(t)=I _(Base)  (7a)I _(Range)(t)=I _(Sensor)(t)−I _(Base)  (7b)

In this case, t designates a present instant and t′ designates aspecific instant that temporally precedes the present instant t.

By way of example, a time interval that corresponds to the firstoperating state (1) is designated by the reference numeral 722 in thediagrams 716, 717, 718 (and also in diagram 719). In this state, theauxiliary current signal I_(Range) 709 is fixed at a constanttime-independent present current value. This current value is defined bythe difference between the sensor current I_(Sensor)(t′) 715 as itflowed at the previous instant t′ and by the predetermined currentintensity value I_(Base) 710 (cf. (6b)). Consequently, the measurementcurrent signal I_(Meas) 708 at the instant t is defined by thedifference between the sensor current signals 715 at the instants t andt′, respectively, plus the predetermined current intensity valueI_(Base) 710 (cf. (6b)). In the operating state (1), as shown in diagram716, the measurement current signal 708 is situated within thepredetermined current intensity range 713.

The operating state (2) is characterized in that the sensor currentsignal 715 generated at the sensor electrode 701 at the instant t,reduced by the predetermined current intensity value I_(Base) 710, formsthe auxiliary current signal 709 at the instant t (cf. (7b)).Consequently, at the instant t, the measurement current signal I_(Meas)is at the predetermined current intensity value I_(Base) 710independently of the sensor current signal I_(Sensor) 715 (cf. (7a)).The predetermined current intensity value I_(Base) 710, which asdiscussed above, is chosen to be 0A in accordance with the exemplaryembodiment described, therefore serves for setting an operating range ofthe measurement current signal I_(Meas) 708. In accordance with thescenario described, wherein I_(Base)=0A is chosen, in the operatingstate (2), the entire sensor current signal I_(Sensor) 715 is theauxiliary current signal I_(Range) 709, so that the measurement currentsignal I_(Meas) 708 disappears.

The operating state (2) is identified in FIG. 7 by way of example by theinstant which is designated by the reference numeral 723 and is depictedin the diagrams 716, 717, 718. Clearly, in this case, on account of theupper limit I_(Base)+ΔI being exceeded on the part of the measurementcurrent signal I_(Meas) 708, the measurement current signal I_(Meas) 708is reset to the predetermined current intensity value 710 and the(additional) current intensity interval ΔI is fed to the auxiliarycurrent signal 709.

The assumption made ideally that the second operating state (2) ischaracterized by a shortest possible period of time, i.e. by an instant723 in the ideal case, often cannot be achieved in reality. The temporalwidth Δt of a real second operating state (2) 723 a is depicted in thediagram 719. However, the time interval Δt shown in the diagram 719 canbe chosen in reality such that the duration of the operating state (2)is negligibly short in relation to the duration of the operating state(1). The finite duration of the second operating state (2) 723 a isunimportant, however, for understanding the functionality of the circuitarrangement 700, so that it is assumed in the rest of the descriptionthat the second operating state (2) 723 can be described essentially bymeans of an instant.

The significance of the time interval Δt is taken up again in thegeneration of a detection pulse (having the temporal length Δt)described below.

The two operating states (1) and (2) 722, 723 are controlled by thecontrol circuit 702 and the voltage-controlled current source 704 in thecircuit arrangement 700.

In order to realize the operating state (2), the current source 704 isdriven by the control circuit 702 by means of a parameter y, which is anelectrical voltage in the case of the circuit arrangement 700. In otherwords, the current source 704 is a voltage-controlled current source.The measurement current signal I_(Meas 708) is transformed by means ofthe current-voltage converter 720 into a variable x, which is anelectrical voltage in accordance with the circuit arrangement 700described in FIG. 7. Said voltage is the output variable of thecurrent-voltage converter 720 and the input variable of a control unit724 of the control circuit 702. The control has the effect that themeasurement current signal is at the predetermined current intensityvalue I_(Base)=0A 710. By means of a signal present at a further input725 of the control unit 724, the control unit 724 is provided with theinformation as to whether the circuit arrangement is to be operated inthe operating state (1) or in the operating state (2).

In order to be able to operate the circuit arrangement according to theinvention in the operating state (1), the control unit 724 is set up insuch a way that the present control value of the voltage y at a previousinstant (for example t′) is held in the case of a corresponding signalat the further input 725. As soon as the auxiliary current signalI_(Range) 709 is determined by this time-independent control value, theoperating state (1) is realized.

A further region of the circuit arrangement 700, namely the thresholdvalue detector 712 of the control circuit 702, the detection unit 711and the counter element 714 defined when the operating state (1) or (2)is realized by the circuit arrangement 700. If the input value x, whichis provided to the threshold value detector 712 by means of thecurrent-voltage converter 720 coupled thereto, exceeds the predeterminedthreshold value 726, then a signal is generated at the output of thethreshold value detector 712 and provided to the input of the detectionunit 711, which signal is such that the detection unit 711 generates apulse 727. The pulse 727 generated by the detection unit 711 is providedto the further input 725 of the control unit 724. This pulse provided tothe control unit 724 informs the control unit 724 of the fact that thepredetermined threshold value 726 has been exceeded at the thresholdvalue detector 712, which is the case if the measurement current signalI_(Meas) 708 exceeds the value I_(Base)+ΔI. The exceeding of thethreshold value 726 is equivalent to the event that the measurementcurrent signal I_(Meas) 708 has exceeded the predetermined currentintensity range 713, i.e. has exceeded the current intensity valueI_(Base)+ΔI.

It must be emphasized that the temporal length of the pulse 727 of thedetection unit 711 corresponds to that length which, in the diagram 719,is designated by Δt as the real length of the second operating state 723a.

It may be expedient for the pulse 727 generated by the detection unit711 to have a shortest possible temporal length Δt→0.

The pulse 727 provided at the further input of the control unit 724 hasthe effect that, during the time duration Δt of the pulse 727, thecontrol unit 724 controls the circuit arrangement 700 in such a way thatthe second operating state (t) is maintained during this time intervalΔt. In the absence of such a pulse 727 at the further input 725 of thecontrol unit 724, the circuit arrangement 700 is in the operating state(1).

The result of the interplay of all the circuit components of the circuitarrangement 700 is illustrated in the diagrams 716, 717, 718. If themeasurement current signal I_(Meas) 708 exceeds the value I_(Base)+ΔI,then the measurement current signal I_(Meas) is reset to thepredetermined current intensity value I_(Base) 710 with the aid of theoperating state (2). After resetting, the measurement current signalI_(Meas) 708 once again rises with a rate determined by the sensorcurrent signal I_(Sensor) 715. The pulses 727 generated by the detectionunit 711 during each reset process are provided not only to the furtherinput 725 of the control unit 724 but also, as shown in FIG. 7, to thecounter element 714. The counter element 714 counts the number of pulsesand the temporal sequence thereof. In other words, the counter element714 registers the number n of pulses in digital form, and it is therebypossible to determine at the counter element 714 what current intensityincrease nΔI has taken place in the measurement time period registered.

In order that said number n is identical to the number of times thesensor current signal I_(Sensor) 715 is exceeded over ΔI segments withinthe time period t₀-t₁, the magnitude Δt should preferably be negligiblyshort in relation to the time between two reset processes. Under thisprecondition, which can often be fulfilled well in practice, it ispossible to determine the current rise m* over n. If n is chosen to besufficiently large or ΔI sufficiently small or the measurement timesufficiently long, then m may be assumed to be as an approximation equalto m*.

It must be emphasized that the described method for processing a sensorcurrent signal 715 provided via a sensor electrode 701 can be employedeven when the time interval Δt, i.e. the length of the pulse 727, is notnegligibly short. In such a scenario, the variable m* that is to beregistered metrologically can be determined in accordance with thefollowing expression:m*(t ₁)=nΔI/(t ₁ −t ₀ −nΔt)  (8)

It must be emphasized that, in a departure from the circuit arrangement700 shown in FIG. 7, instead of providing the counter element 714, it isalso possible directly to register the frequency of the pulses 727 atthe output of the detection unit 711. This frequency contains theinformation of the sensor current signal I_(Sensor) 715.

The method for processing a sensor current signal I_(Sensor) 715provided via the sensor electrode 701, which method is based on the useof the circuit arrangement 700, has the following steps in summary: ifthe measurement current signal I_(Meas) 708 flowing into the controlcircuit 702 via its input 703 is outside the predetermined currentintensity range 713, the control circuit 702 controls the current source704 in such a way that the current source 704 sets the electricalauxiliary current signal I_(Range) 709 generated by it in such a waythat the electric measurement current signal I_(Meas) 708 flowing intothe input 703 of the control circuit 702 is brought to the predeterminedcurrent intensity value I_(Base) 710. If the measurement current signalI_(Meas) 708 flowing into the control circuit 702 via its input 703 iswithin the predetermined current intensity range 713, the controlcircuit 702 controls the current source 704 in such a way that thecurrent source 704 holds the electric auxiliary current signal I_(Range)709 generated by it at the present value.

Furthermore, the detection unit 711 detects the event that themeasurement current signal I_(Meas) 708 flowing into the control circuit702 via its input 703 is outside the predetermined current intensityrange 713.

A description is given below, with reference to figure BA, FIG. 8B, ofhow the principle according to the invention functions if the sensorcurrent signal I_(Sensor) deviates from its ideal linear form (cf. FIG.6) and signal fluctuations (for example on account of noise effects)occur.

FIG. 8A shows a diagram 800, along the abscissa of which the time t 802is plotted, and along the ordinate of which the electric sensor current801 is plotted. As shown in FIG. 8A, the sensor current-time curveprofile 803 is not linear, but rather has fluctuations.

FIG. 8B shows a further diagram 810, along the abscissa of which thetime t 812 is plotted, which corresponds to the time 802 plotted infigure BA. The electric measurement current 811 is plotted along theordinate of the further diagram 810. Furthermore,

FIG. 8B plots the measurement current-time curve profile 813 as resultsduring the operation of the circuit arrangement 700 according to theinvention for the case where the sensor current-time curve profile 803illustrated in FIG. 8A is present.

Furthermore, FIG. 8A shows a current intensity interval ΔI 804. Thepredetermined current intensity range essential for the functionality ofthe circuit arrangement according to the invention, that is to say therange between a predetermined current intensity value I_(Base) 814 andI_(Base)+ΔI, is designated by the reference numeral 815 in FIG. 8B.

After each further occasion that the electric sensor current I_(Sensor)exceeds a current intensity interval ΔI 804, the electric measurementcurrent 811 is reset. These reset points 816 are shown in FIG. 8B, andtheir number corresponds to the characteristic variable n introducedabove. What is crucial for the functionality of the circuit arrangementfor indirectly registering the electric sensor current 801 is that whena specific current interval line is repeatedly exceeded, precisely onereset and thus counting process is initiated. This phenomenon can becomprehended if a measurement interval of the sensor current 805 iscompared with a measurement interval of the measurement current 817.Within the time period defined by the measurement intervals 805, 817,the current interval line 806 shown in FIG. 8A is multiply exceeded andundershot in the measurement interval of the sensor current 805 (forexample on account of noise effects or the like). FIG. 8B reveals,however, that in the measurement interval of the measurement current817, a reset point 816 can be seen only on the first occasion when thecurrent interval line 806 is exceeded. In other words, a pulse that iscounted by a counter element is output only upon the first occasion whena current interval line 806 is exceeded. All further occasions when thesame current interval line 806 is exceeded no longer reach the thresholdvalue I_(Base)+ΔI in FIG. 8B.

The method for processing a current signal provided via a sensorelectrode, which method is based on the circuit arrangement according tothe invention, is thus robust with respect to signal fluctuations. Theaveraging effect achieved by means of the method is furthermoreadvantageous in the determination of the current curve rise.

The measurement current-time curve profile 813 shown in FIG. 8B showsthat the electric measurement current 811 is upwardly limited on accountof the progressive resetting when the current value I_(Base)+ΔI isexceeded. However, a lower limitation of the current is not given.

FIG. 9A shows a circuit arrangement 900 in accordance with a thirdexemplary embodiment of the invention, which represents a development ofthe circuit arrangement 700 shown in FIG. 7. Those elements of thecircuit arrangement 900 from FIG. 9A which are identical to componentsof the circuit arrangement 700 are provided with the same referencesymbols in FIG. 9A and are not explained in any more detail below.

The circuit arrangement 900 shown in FIG. 9A has the advantageousdevelopment in comparison with the circuit arrangement 700 shown in FIG.7 that the electric measurement current is also downwardly limited.

In contrast to the circuit arrangement 700 shown in FIG. 7, the circuitarrangement 900 has the following components: a control circuit 901, thecontrol unit 905 of which has a first further input 906 a and a secondfurther input 906 b instead of the further input 725 from FIG. 7. Thedetection unit of the circuit arrangement 900 shown in FIG. 9A has afirst region of the detection unit 902 a and a second region of thedetection unit 902 b. The threshold value detector of the circuitarrangement 900 has a first region of the threshold value detector 903 aand a second region of the threshold value detector 903 b. The voltagesignal x provided by the current-voltage converter 720 at the outputthereof is provided to the control unit 905 and both to the first regionof the threshold value detector 903 a and to the second region of thethreshold value detector 903 b.

The first region of the threshold value detector 903 a essentiallyfulfils the same functionality as the threshold value detector 712 shownin FIG. 7. If the voltage signal x provided to the input of the firstregion of the threshold value detector 903 a by the current-voltageconverter 720 exceeds a first predetermined threshold value 907 a of thefirst region of the threshold value detector 903 a, then a correspondingsignal is communicated from the output of the first region of thethreshold value detector 903 a to the input of the first region of thedetection unit 902 a, said input being coupled to said output. The firstregion of the detection unit 902 a has an output that is coupled to thefirst further input 906 a of the control unit 905 and that is coupled tothe first input 904 a of the counter element 904. The first region ofthe detection unit 902 a generates a first pulse 908 a, which isprovided to the first further input 906 a of the control unit 905 andwhich is provided to the first input 904 a of the counter element 904.The first pulse signal 908 a has the effect, at the first further input906 a of the control unit 905, that the measurement current signalI_(Meas) 708 is reset from the value I_(Base)+ΔI to the value I_(Base).The first pulse 908 a has the effect, at the first input 904 a of thecounter element 904, that the counter reading of the counter element 904is increased by a predetermined value (for example by “1”). In thisrespect, the functionality of the circuit arrangement 900 corresponds tothat of the circuit arrangement 700.

Furthermore, the voltage signal x that is generated by thecurrent-voltage converter 720 and is characteristic of the presentmeasurement current signal 708 is provided to the second region of thethreshold value detector 903 b at the input thereof. If the voltagesignal x falls below the second predetermined threshold value 907 b ofthe second region of the threshold value detector 903 b, then acorresponding electric signal is generated at the output of the secondregion of the threshold value detector 903 b, which is coupled to theinput of the second region of the detection unit 902 b, and saidelectric signal is communicated to the input of the second region of thedetection unit 902 b. In this case, a second pulse 908 b is generated bythe second region of the detection unit 902 b. The output of the secondregion of the detection unit 902 b is coupled both to the second furtherinput 906 b of the control unit 905 and to the second input 904 b of thecounter element 904. Therefore, if the second pulse 908 b is generatedat the second region of the detection unit 902 b, said second pulse isprovided to these two inputs. The scenario described corresponds to thescenario that is designated by the instant 927 in FIG. 9 b and in thecase of which the measurement current signal 708 reaches the lower limitI_(Base)−ΔI of the predetermined current intensity range 925. The secondpulse signal 908 b provided to the control unit 905 at the secondfurther input 906 b thereof effects control of the current source 704 insuch a way that the measurement signal I_(Meas) 708 is reset to thepredetermined current intensity value I_(Base) 924. The second pulse 908b provided to the second input 904 b of the counter element 904 has theeffect there that the counter reading of the counter element 904 b isdecreased by a predetermined value (for example by “1”). A correctsummation of the reset pulses is thereby realized, since the reset pulseeffected at the instant 927 is not caused by an increase in the sensorcurrent by a further current intensity range 804, but rather a decreasein the current signal that can be attributed for example to noiseeffects.

In other words, the circuit arrangement 900 from FIG. 9A realizes alimitation of the measurement current signal I_(Meas) to thepredetermined current intensity range 925 between I_(Base)−ΔI andI_(Base)+ΔI. The circuit arrangement shown in FIG. 9A thus represents anadvantageous development of the circuit arrangement 700, since alowering of the measurement current signal 708 can also be detectedcorrectly by means of the circuit arrangement 900. The counter element904 of the circuit arrangement 900 is designed as an up/down counter.

The functionality of the circuit arrangement 900 from FIG. 9A isdescribed below with reference to the diagram 920 from FIG. 9B.

The diagram 920 has an abscissa, along which the time 922 is plotted.The electric measurement current 921 is plotted along the ordinate.Furthermore, the diagram shows the measurement current-time curveprofile 923 as is obtained using the circuit arrangement 900 shown inFIG. 9A in the case of a sensor current-time curve profile 803 as isshown in FIG. 8A. The electric measurement current 921 remains withinthe predetermined current intensity range 925 around the predeterminedcurrent intensity value I_(Base) 924 with a bandwidth ΔI extendingupward and downward. FIG. 9 b furthermore shows first reset points 926 aand a second reset point 926 b. A comparison of the measurement currenttime curve profile 923 with the sensor current-time curve profile 803shows that the first reset points reflect a respective increase in thesensor current 801 by a further current intensity interval 804, whereasthe reset point 926 b symbolizes the decrease—which can be recorded atthe instant 927—in the sensor current 801 by a current intensityinterval ΔI 804. The second pulses 908 b generated by the “+ΔI” eventare fed to the up input 904 a of the counter element 904, and the secondpulses 908 b generated by the “−ΔI” event are fed to the down input 904b of the counter element 904. Consequently, the counter reading 928increases by the predetermined value of “1” in the case of each firstreset point 926 a, whereas the counter, reading 928 decreases by “1” inthe case of the second reset point 926 b. The circuit arrangement 900shown in FIG. 9A consequently enables a completely correct summation ofthe pulses even in a scenario in which the sensor current decreasesoccasionally on account of undesirable effects.

A detailed description is given below, with reference to FIG. 10A, FIG.10B, of a fourth preferred exemplary embodiment of a circuit arrangement1000 according to the invention.

The circuit arrangement 1000 shown in FIG. 10A represents a circuitryrealization of the circuit arrangement 700 shown in FIG. 7. Therefore,those circuit blocks of the circuit arrangement 1000 which areconfigured as an equivalent element in the circuit arrangement 700 areprovided with the same reference numerals.

The sensor electrode 701, proceeding from which the sensor currentsignal 715 flows, is coupled to one source-drain region of a first p-MOStransistor 1001, which forms the current-voltage converter 720.Furthermore, the electrical node 721 is coupled to one source-drainregion of a second p-MOS transistor 1002. The measurement current signalI_(Meas) 708 flows between the electrical node 721 and the first p-MOStransistor 1001, and the auxiliary current signal I_(Range) flowsbetween the node 721 and one source-drain region of the second p-MOStransistor 1002. The gate region of the first p-MOS transistor 1001 iscoupled to a second electrical node 1003. The second electrical node1003 is coupled to a third electrical node 1004. The third electricalnode 1004 is coupled to the output of a first operational amplifier1005. Furthermore, the third electrical node 1004 is coupled to onesource-drain region of a third p-MOS transistor 1006. The noninvertedinput of the first operational amplifier 1005 is coupled to theelectrical node 721. The noninverted input of the first operationalamplifier 1005 is coupled to a first reference voltage source 1007. Theother source-drain region of the first p-MOS transistor 1001 is coupledto one source-drain region of a fourth p-MOS transistor 1008. The othersource-drain region of the fourth p-MOS transistor 1008 is coupled to asupply voltage source 1009. The gate region of the fourth p-MOStransistor 1008 is coupled to a fourth electrical node 1010. The fourthelectrical node 1010 is coupled to the output of the detection unit 711and to the input of the counter element 714. The second electrical node1003 is furthermore coupled to the inverted input of a secondoperational amplifier 1011. The noninverted input of the secondoperational amplifier 1011 is coupled to a second reference voltagesource 1012. The output of the second operational amplifier 1011, atwhich a first output signal 1013 may be present, is coupled to the inputof the detection unit 711. A further output of the detection unit 711 iscoupled to the gate region of the third p-MOS transistor 1006. The othersource-drain region of the third p-MOS transistor 1006 is coupled to afifth electrical node 1014. The fifth electrical node 1014 is coupled tothe gate region of the second p-MOS transistor 1002 and to a storagecapacitor 1015. The storage capacitor 1015 is furthermore coupled to asixth electrical node 1016. The sixth electrical node 1016 isfurthermore coupled to the other source-drain region of the second p-MOStransistor 2002. The sixth electrical node 1016 is furthermore coupledto the supply voltage source 1009.

The second p-MOS transistor 1002 and the storage capacitor 1015connected in parallel therewith form the voltage-controlled currentsource 704. The first reference voltage source 1007, the firstoperational amplifier 1005, the third electrical node 1004 and the thirdp-MOS transistor 1006 form the control unit 725.

The second operational amplifier 1011 and the second reference voltagesource 1012 form the threshold value detector 712. As indicated in FIG.10A, the detection unit 711 is set up in such a way that, in a scenarioin which a first output signal 1013 is provided to the input of thedetection unit 711 by the threshold value detector 712, the detectionunit 711 provides a first pulse 1017 to the counter element 714 and tothe gate region of the fourth p-MOS transistor 1008. Furthermore, thedetection unit 711 is designed in such a way that, in a scenario inwhich a first output signal 1013 is provided to the detection unit 711by the threshold value detector 712, the detection unit 711 provides asecond pulse 1018 to the gate region of the third p-MOS transistor 1006.

The precise configuration of the counter 714 is not shown in FIG. 10A.The counter 714 may be for example a synchronous binary counterconstructed from JK flip-flops.

The precise construction of the detection unit 711 is explained indetail below with reference to FIG. 10B.

It should be pointed out that the circuit arrangement 1000 shown in FIG.10A, in contrast to the circuit arrangement 700 shown in FIG. 7, has anelectrical coupling means 1019 for coupling the electrical node 721 tothe control unit 725, more precisely to the noninverted input of thefirst operational amplifier 1005 of the control unit 725. In order toachieve the function of the electrical node 721 as a summation point inaccordance with equation (5), it is to be ensured that the currentdisappears in this additional line which is formed by means of theelectrical coupling means 1019. This requirement is fulfilled well ifthe transistors of the input differential stage of the first operationalamplifier 1005 are designed as MOS transistors.

Two different active control loops 1020, 1021 result in a mannerdependent on the conduction state of the third and fourth p-MOStransistors 1006, 1008.

The output of the first operational amplifier 1005 is fed back to thenoninverted input in inverting fashion by means of the second or firstp-MOS transistor 1002, 1001, respectively. The open-loop gain of thefirst operational amplifier 1005 is designated by A1 hereinafter. Thefollowing then holds true as long as the feedback ensures that the firstoperational amplifier 1005 does not enter into limitation:V _(Out) =A1(V _(K) −V _(Bias))  (9)

V_(Out) is the voltage present at the output of the first operationalamplifier 1005. V_(K) is the voltage present at the electrical node 721and therefore at the noninverted input of the first operationalamplifier 1005, and V_(Bias) is the electrical voltage provided to theinverted input of the first operational amplifier by the first referencevoltage source 1007. The following then results after simpletransformation:V _(K) =V _(Bias) +V _(Out) /A1  (10)

For a large open-loop gain (A1→∞), it then follows from equation (10)that the voltage present at the electrical node 721 is equal to theelectrical voltage provided at the inverted input of the firstoperational amplifier 1005 by the first reference voltage source 1007.

The potential at the electrical node 721 is thus adjusted to the valueV_(Bias) prescribed by the first reference voltage source 1007 at theinverted input of the first operational amplifier 1005. This voltagevalue, which simultaneously determines the electrical potential at thesensor electrode 701, is necessary in order to enable the redoxrecycling process.

The first control state 1020 and the second control state 1021 aredescribed in more detail below.

Firstly a description is given of the first control loop 1020 whichcorresponds to the operating state of the circuit arrangement accordingto the invention that is designated above by operating state (1).

This case corresponds to the scenario wherein the detection unit 711does not generate a first pulse 1017 and a second pulse 1018 at itsoutput and at its further output. The lack of provision of a first pulse1017, which, in accordance with FIG. 10A, represents a logic value “0”in a departure from a logic value “1” that otherwise prevails inconstant fashion, means that the gate region of the fourth p-MOStransistor 1008 is conducting. Since the detection unit 711 does notgenerate a second pulse 1018, which, as shown in FIG. 10A, wouldgenerate the logic value “1” proceeding from a logic value “0” for theduration of the pulse, the gate region of the third p-MOS transistor1006 is not conducting. In accordance with the first control state 1020,the gate region of the third p-MOS transistor 1006 is thusnonconducting, whereas the gate region of the fourth p-MOS transistor1008 is conducting.

Since the gate region of the third p-MOS transistor 1006 is notconducting, a constant electrical voltage is present at the storagecapacitor 1015 and thus at the gate region of the second p-MOStransistor 1002. Since a constant electrical voltage is likewise presentat the electrical node 721, a time-independent auxiliary currentI_(Range) 709 results through the gate region of the second p-MOStransistor 1002. The temporally changed sensor current I_(Sensor) 715therefore flows through the gate region of the first p-MOS transistor1001. The electrical voltage at the output of the first operationalamplifier 1005 is established such that the electrical voltage at thegate region of the first p-MOS transistor 1001 enables the requiredcurrent flow.

A description is given below of the second control loop 1021, whichcorresponds to the operating state of the circuit arrangement 1000 thatis designated as operating state (2) above. In accordance with thisscenario, the detection unit 711, on account of a corresponding firstoutput signal 1013 at its input, generates a first pulse 1017 and asecond pulse 1018 at its two outputs. The first pulse 1018, as shown inFIG. 10A, is set up in such a way that the gate region of the thirdp-MOS transistor 1006 thereby becomes conducting. By contrast, the firstpulse 1017, as shown in FIG. 10A, is set up in such a way that, duringthe pulse duration, the gate region of the fourth p-MOS transistor 1008becomes nonconducting. Since the gate region of the fourth p-MOStransistor 1008 is nonconducting, a vanishing measurement currentI_(Meas) 7008 (I_(Meas)=0) results independently of the output voltageof the first operational amplifier 1005. By contrast, the gate region ofthe third p-MOS transistor 1006 is in the conducting state, and, inaccordance with this scenario, the output voltage of the firstoperational amplifier 1005 is the gate voltage of the second p-MOStransistor 1002, and therefore controls the auxiliary current I_(Range)that flows through the gate region of the second p-MOS transistor 1002.The gate voltage of the second p-MOS transistor 1002 is controlled bythe circuit arrangement 1000 in such a way that the auxiliary currentI_(Range) 709 is equal to the sensor current I_(Sensor) 715. The entiresensor current of the sensor electrode 701 is thus conducted away intothe range channel.

A changeover in the operating state of the circuit arrangement 1000 fromthe second operating state 1021 to the first operating state 1020therefore corresponds to a change in the conduction state of the thirdand fourth p-MOS transistors 1006, 1008 proceeding from a state in whichthe third p-MOS transistor 1006 is conducting and the fourth p-MOStransistor 1008 is nonconducting, through to a state in which the thirdp-MOS transistor 1006 is nonconducting and the fourth p-MOS transistor1008 is conducting.

If the third p-MOS transistor 1006 is switched such that it isnonconducting, by means of the electrical voltage at the storagecapacitor 1015, the auxiliary current I_(Range) 709 is stored by meansof the second p-MOS transistor 1002. Therefore, in the first operatingstate 1020, the measurement current I_(Meas) 708 is the sensor currentI_(Sensor) 715 minus the stored auxiliary current I_(Range) 709.

The third and fourth p-MOS transistors 1006, 1008 are driven by means ofthe second pulse 1018 and the first pulse 1017 of the detection unit711. In the first operating state 1020 of the circuit arrangement 1000,an increase in the sensor current I_(Sensor) 715 leads to a largermeasurement current I_(Meas) 708. The gate voltage of the first p-MOStransistor 1001 decreases correspondingly. If the gate voltage fallsbelow the value of the voltage of the second reference voltage source1012 of the second operational amplifier 1011, then a positive edge isgenerated at the output of the second operational amplifier 1011 (whichfunctions as a comparator). Said edge excites the detection unit 711 togenerate a pulse. As already discussed above, the detection unit is setup in such a way that, in the normal state, the two outputs of thedetection unit 711 switch the operating state (1) 1020. In other words,the gate region of the third p-MOS transistor 1006 is nonconducting,whereas the gate region of the fourth p-MOS transistor 1008 isconducting. A first pulse 1017 and a second pulse 1018 are generated inthe detection unit 711 and produce the second operating state (2) for apredetermined time interval Δt. In accordance with this scenario, thegate region of the third p-MOS transistor 1006 is conducting, whereasthe gate region of the fourth p-MOS transistor 1008 is nonconducting. Inthis second operating state, the measurement current I_(Meas) 708 isreturned to the value 0, and at the same time a new auxiliary currentI_(Range) 709 is defined. The number of reset processes is realized byregistering the number of pulses by means of the counter element 714,the number and the temporal sequence of the pulses being storeddigitally in the counter element 714.

An exemplary embodiment of the detection unit 711 according to theinvention is described below with reference to FIG. 10B.

The exemplary embodiment of the detection unit 711 as described in FIG.10B shows how, proceeding from the first output signal 1013 of thethreshold value detector 712, it is possible to generate a pulse havingthe temporal length Δt, which provides a signal having a logic value “1”for a time period Δt, whereas the signal assumes a logic value “0”before the pulse and after the pulse. Such a pulse corresponds to thepulse 1018 shown in FIG. 10A. A first pulse 1017 from FIG. 10A may begenerated for example by firstly generating a pulse of the type of thesecond pulse 1018 and subtracting this pulse from a constant signal.

The detection unit 711 shown in FIG. 10B has a flip-flop 1050 having afirst input 1051, a second input 1052 and an output 1053. The firstinput 1051 is the edge-sensitive input of the flip-flop 1050, and thefirst output signal 1013 defined and shown in FIG. 10A is applied tosaid input. As a result, the output 1053 of the flip-flop 1050 isbrought from a logic value “0” to a logic value “1”. The output 1053 ofthe flip-flop 1050 is coupled to an electrical node 1054. Saidelectrical node is coupled to a nonreactive resistor 1055. Thenonreactive resistor 1055 is coupled to a second electrical node 1056.The second electrical node 1056 is coupled to a capacitor 1057.Furthermore, the second electrical node 1056 is coupled to a firstamplifier stage 1058, and the first amplifier stage 1058 is coupled to asecond amplifier stage 1059. The second amplifier stage 1059 is coupledto the second input 1052 of the flip-flop 1050. The functionality of theamplifier stages 1058, 1059 is to be seen in the fact that defined logiclevels are present at the second input 1052 of the flip-flop 1050. Theoutput edge at the output 1053 of the flip-flop 1050 is delayed by meansof the RC element formed from the nonreactive resistor 1056 and thecapacitor 1057 and is used as a reset for the flip-flop 1050. What isgenerated as a result is a pulse having the length Δt proportional toRC, where R is the resistance of the nonreactive resistor 1055 and C isthe capacitance of the capacitor 1057. Therefore, the pulse duration isessentially determined by an RC element.

The following publications are cited in this document:

-   [1] Hintsche, R, Paeschke, M, Uhlig, A, Seitz, R (1997)    “Microbiosensors using Electrodes made in Si-technoloty”, Frontiers    in Biosensorics, Fundamental Aspects, Scheller, F W, Schuber L, F,    Fedrowitz, J (eds.), Birkhauser Verlag Basle, Switzerland, pp.    267-283-   [2] van Gerwen, P (1997) “Nanoscaled interdigitated Electrode Arrays    for Biochemical Sensors”, IEEE, International Conference on    Solid-State Sensors and Actuators, Jun. 16-19, 1997, Chicago, pp.    907-910-   [3] Paeschke, M, Dietrich, F, Uhlig, A, Hintsche, R (1996)    “Voltammetric Multichannel Measurements Using Silicon Fabricated    Microelectrode Arrays”, Electroanalysis, Vol. 7, No. 1, pp. 1-8-   [4] Uster, M, Loeliger, T. Guggenbühl, W, Jäckel, H (1999)    “Integrating ADC Using a Single Transistor as Integrator and    Amplifier for Very Low (1fA Minimum) Input Currents”, Advanced A/D    and D/A Conversion Techniques and Their Applications, Strathclyde    University Conference (Great Britain) Jul. 27-28, 1999, Conference    Publication No. 466, pp. 06-89, IEE

List of Reference Symbols

-   100 Circuit arrangement-   101 Sensor electrode-   102 Control circuit-   103 Input-   104 Current source-   105 Control input-   106 Control output-   107 Output-   108 First current signal-   109 Second current signal-   110 Detection unit-   111 Capture molecules-   112 Molecules to be registered-   113 Enzymes-   114 Electrically charged particles-   115 Third current signal-   200 Sensor-   201 Electrode-   202 Electrode-   203 Insulator-   204 Electrode terminal-   205 Electrode terminal-   206 DNA probe molecule-   207 Electrolyte-   208 DNA strands-   300 Interdigital electrode-   400 Biosensor-   401 First electrode-   402 Second electrode-   403 Insulator layer-   404 Holding region of first electrode-   405 DNA probe molecule-   406 Electrolyte-   407 DNA strand-   408 Enzyme-   409 Cleavable molecule-   410 Negatively charged first partial molecule-   411 Arrow-   412 Further solution-   413 Oxidized first partial molecule-   414 Reduced first partial molecule-   500 Diagram-   501 Electric current-   502 Time-   503 Current-time curve profile-   504 Offset current-   600 Diagram-   601 Electric sensor current-   602 Time-   603 Current-time curve profile-   604 Offset current-   605 Gradient of the current-time curve profile-   700 Circuit arrangement-   701 Sensor electrode-   702 Control circuit-   703 Input-   704 Current source-   705 Control input-   706 Control output-   707 Output-   708 Measurement current signal-   709 Auxiliary current signal-   710 Predetermined current intensity value-   711 Detection unit-   712 Threshold value detector-   713 Predetermined current intensity range-   714 Counter element-   715 Sensor current signal-   716 Diagram-   717 Diagram-   718 Diagram-   719 Diagram-   720 Current-voltage converter-   721 Electrical node-   722 First operating state-   723 Second operating state-   723 a Real second operating state-   724 Control unit-   725 Further input-   726 Predetermined threshold value-   727 Pulse-   728 Diagram-   800 Diagram-   801 Electric sensor current-   802 Time-   803 Sensor current-time curve profile-   804 Current intensity interval-   805 Measurement interval of the sensor current-   806 Current interval line-   810 Diagram-   811 Electric measurement current-   812 Time-   813 Measurement current-time curve profile-   814 Predetermined current intensity value-   815 Predetermined current intensity range-   816 Reset points-   817 Measurement interval of the measurement current-   900 Circuit arrangement-   901 Control circuit-   902 a First region of the detection unit-   902 b Second region of the detection unit-   903 a First region of the threshold value detector-   903 b Second region of the threshold value detector-   904 Counter element-   904 a First input-   904 b Second input-   905 Control unit-   906 a First further input-   906 b Second further input-   907 a First predetermined threshold value-   907 b Second predetermined threshold value-   908 a First pulse-   908 b Second pulse-   920 Diagram-   921 Electric measurement current-   922 Time-   923 Measurement current-time curve profile-   924 Predetermined current intensity value-   925 Predetermined current intensity range-   926 a First reset points-   926 b Second reset point-   927 Instant-   928 Counter reading-   1000 Circuit arrangement-   1001 First p-MOS transistor-   1002 Second p-MOS transistor-   1003 Second electrical node-   1004 Third electrical node-   1005 First operational amplifier-   1006 Third p-MOS transistor-   1007 First reference voltage source-   1008 Fourth p-MOS transistor-   1009 Supply voltage source-   1010 Fourth electrical node-   1011 Second operational amplifier-   1012 Second reference voltage source-   1013 First output signal-   1014 Fifth electrical node-   1015 Storage capacitor-   1016 Sixth electrical node-   1017 First pulse-   1018 Second pulse-   1019 Electrical coupling means-   1020 First control loop-   1021 Second control loop-   1050 Flip-flop-   1051 First input-   1052 Second input-   1053 Output-   1054 Electrical node-   1055 Nonreactive resistor-   1056 Second electrical node-   1057 Capacitor-   1058 First inverter stage-   1059 Second inverter stage

1-17. (canceled)
 18. A circuit arrangement comprising: a sensorelectrode; a control circuit coupled to the sensor electrode via aninput; a current source having a control input which is coupled to acontrol output of the control circuit in such a way that the currentsource can be controlled by the control circuit, and which is coupled tothe sensor electrode via an output; the control circuit arranged in sucha way that if a current signal provided to the input of the controlcircuit is outside a predetermined current intensity range, the controlcircuit controls the current source in such a way that the currentsource sets the electric current generated by it in such a way that theelectric current flowing into the input of the control circuit isbrought to a predetermined current intensity value; is within thepredetermined current intensity range, the control circuit controls thecurrent source in such a way that the current source holds the electriccurrent generated by it at the present value; and a detection unit,which can detect the event that the current signal flowing into thecontrol circuit via its input is outside the predetermined currentintensity range.
 19. The circuit arrangement of claim 18, furthercomprising a counter element electrically coupled to the detection unitand which is set up in such a way that it counts a number or a temporalsequence of the events detected by the detection unit.
 20. The circuitarrangement of claim 19, wherein the counter element is set up in such away that if the current signal provided to the input of the controlcircuit exceeds an upper limit of the predetermined current intensityrange, the counter reading is increased by a predetermined value. 21.The circuit arrangement of claim 20 wherein the counter element is setup in such a way that if the current signal provided to the input of thecontrol circuit falls below a lower limit of the predetermined currentintensity range, the counter reading is decreased by a predeterminedvalue.
 22. The circuit arrangement of claim 19, wherein the counterelement is set up in such a way that if the current signal provided tothe input of the control circuit exceeds an upper limit of thepredetermined current intensity range, the counter reading is decreasedby a predetermined value.
 23. The circuit arrangement of claim 22,wherein the counter element is set up in such a way that if the currentsignal provided to the input of the control circuit falls below a lowerlimit of the predetermined current intensity range, the counter readingis increased by a predetermined value.
 24. The circuit arrangement ofclaim 18 in which the current source is a voltage-controlled currentsource.
 25. The circuit arrangement of claim 18 wherein the controlcircuit comprises: a current-voltage converter at its input set up insuch a way that the current present at the input of the control circuitis converted into an electrical voltage signal by means
 26. The circuitarrangement of claim 18 wherein the sensor electrode, the controlcircuit, the current source and the detection unit are combined in acommon integrated circuit.
 27. A redox recycling sensor comprising thecircuit arrangement of claims
 18. 28. A method for processing a currentsignal the method comprising: detecting a current signal at an input ofa control circuit; generating an electric current at a current source;if the current signal at the input of the control circuit is outside thepredetermined current intensity range, the control circuit controls thecurrent source in such a way that the current source sets the electriccurrent generated by it in such a way that the current detected at theinput of the control circuit is brought to a predetermined currentintensity value; is within the predetermined current intensity range,the control circuit controls the current source in such a way that thecurrent source holds the electric current generated by it at a presentvalue; detecting as an event the current signal being outside thepredetermined current intensity range flowing into input of the controlcircuit.
 29. The method of claim 28 further comprising: counting in acounter a number or a temporal sequence of the events.
 30. The method ofclaim 29 further comprising: if the current signal detected at the inputof the control circuit exceeds an upper limit of the predeterminedcurrent intensity range, increasing the counter by a predeterminedvalue.
 31. The method of claim 30 further comprising: if the currentsignal detected at the input of the control circuit falls below a lowerlimit of the predetermined current intensity range, decreasing thecounter by a predetermined value.
 32. The method as claimed in claim 29further comprising: if the current signal detected at the input of thecontrol circuit exceeds an upper limit of the predetermined currentintensity range, decreasing the counter by a predetermined value. 33.The method as claimed in claim 32 further comprising: if the currentsignal detected at the input of the control circuit falls below a lowerlimit of the predetermined current intensity range, increasing thecounter by a predetermined value.
 34. A circuit arrangement for a redoxrecycling sensor comprising: a sensor electrode configured to sensehybridization of a DNA strand with an enzyme label at a capture moleculeimmolized on the sensor electrode, the enzyme generating free chargecarriers that bring about a current flow at the sensor electrode when acorrespondingly suitable liquid is added; a control circuit having aninput coupled to the sensor electrode for detecting the current flow atthe sensor electrode as a measured current; a current source having acontrol input which is coupled to a control output of the controlcircuit in such a way that the current source can be controlled by thecontrol circuit, and which is coupled to the sensor electrode via anoutput; the control circuit arranged in such a way that if the measuredcurrent is outside a predetermined current intensity range, the controlcircuit controls the current source in such a way that the currentsource sets a range current generated by it in such a way that themeasured current detected at the input of the control circuit is broughtto a predetermined current intensity value; is within the predeterminedcurrent intensity range, the control circuit controls the current sourcein such a way that the current source holds the range current generatedby it at the present value; and a detection unit, which can detect theevent that the measured current at the control circuit input is outsidethe predetermined current intensity range.